#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main() {
    int n = 0;
    long long s = 0;
    scanf("%d", &n);
    int i = 0;
    for (i = 1; i <= n; i++) {
        s += i;
    }
    printf("%ld", s);
    return 0;
}